Administration of ultrasonically nebulized mist to 17 patients with obstructive lung disease resulted in a temporary deterioration of mechanical lung function with decreases in vital capacity (VC), forced expired volume in one second expressed as a percentage of VC (FEV(1)%), and compliance and with increased inspiratory and expiratory airway resistance. Despite hyperventilation there was an associated decrease in arterial oxygen tension. Although concomitant administration of a bronchodilator afforded protection against the bronchospastic reaction, blood gas derangements were still provoked.